Trees plus man-made emissions create dangerous particulate matter

April 09, 2013

A new study has identified an unexpected source of particulate matter creation that potentially could produce damaging effects on human beings – trees.The study found that isoprene, which is the most abundant hydrocarbon emitted from trees, once oxidized by our atmosphere, is reacting with human-made nitrogen oxides to create unforeseen particulate matter.

The findings were published by the recent Proceedings of the National Science Academy (PNAS) in a study titled “Epoxide as a precursor to secondary organic aerosol formation from isoprene photooxidation in the presence of nitrogen oxides.”

Dr. Jason Surratt

The study, led by Jason Surratt, PhD, assistant professor of environmental sciences and engineering at the Gillings School of Global Public Health at the University of North Carolina, presents a dramatic new wrinkle in the arguments for reducing combustion emissions worldwide.

“Isoprene is primarily emitted from trees and is the largest single non-methane hydrocarbon emission into Earth’s atmosphere,” Surratt said. “There is very little we can do to control this, short of cutting down all the trees – which no one wants to do and which would cause a whole host of other environmental problems. But human-made pollutant emissions that come from cars, trucks, aircraft, coal plants and other large-scale sources are controllable.”

Isoprene emissions were not thought to be a contributor to the creation of fine particulate matter. The study, however, used field observations, computational chemistry calculations and community multiscale air-quality (CMAQ) model simulations to confirm the chain of evidence of isoprene photooxidation – that is, oxidation caused by chemically reacting with the sun’s rays – which then interacts with nitrogen oxides produced by human-made combustion sources to create particulate matter. This fine particulate matter potentially could lead to serious respiratory ailments such as asthma.

“The evidence we generated points to something that likely contributes to significant public health risks across the planet in areas where tree emissions such as isoprene combine with human-made pollutants,” Surratt says. “This could be a paradigm shift in the way atmospheric chemists look at combustion emissions, and perhaps a re-thinking in general by anyone interested in climate change and health.”